An air filter is provided in each inlet of, for example, clean rooms, air conditioning equipment, gas turbines, and steam turbines. An air filter suitable for these purposes is a filter unit panel in which a plurality of filter units, each having a filter medium and a frame body for supporting it, are joined together with their outer peripheral surfaces being in contact with each other. JP 2005-177641 A discloses in FIG. 2 an example of a filter unit panel in which filter units, each having a frame body (supporting frame) made of a resin member, are joined together.
A filter unit panel further is provided with an outer frame that surrounds the outer peripheral surface of the panel in some cases. The outer frame protects the filter units, increases the strength of the entire panel, and facilitates installing the filter units. Conventionally, a metal member such as aluminum or a wood member has been used for the outer frame.